This paper reports the results of a preliminary experiment to test the
hypothesis that a system of underground shelters would be a way of improving the
environment of the rabbit, as compared with conventional raised cages, and thus make it
possible to increase productivity in a tropical climate. The study was done with the
cooperation of 30 small scale farmers in Ha Tay and Hai Hung provinces in North Vietnam.

All the performance parameters were significantly improved in rabbits
housed in the underground shelters compared with the cages. The does in underground
shelters were 8% heavier after 2 months in the experiment, they gave birth to 39% more
offspring and weaned 60% more than those in cages. Survival rate to weaning of the
offspring was improved by 16%.

During the growing-fattening phase, the rabbits in underground shelters
were 17% heavier after 1 month and 19% heavier after 3 months with average growth rates
that were 20% greater.

It is concluded that the underground shelter system of housing is
especially suitable for rabbit production for small scale farmers in tropical regions.

Rabbit breeding is practised in almost all developing countries and
contributes to family nutrition and economy, through the availability of a source of
animal protein, as well as through extra income by sale of animals. Rabbit production has
been developed in Vietnam based on the conventional system of cages raised above the
ground. The major constraints of this housing system are low reproduction due to high
temperatures in summer (30-35 ºC) and high mortality of the offspring due to cold (12-15
ºC) and wet weather in winter. The suitable ambient environment for rabbit production in
Vietnam is a temperature range of 18-28 ºC and humidity between 80 and 86% (Nguyen Quang
Suc 1985).

The greatest disadvantage of the cage system is that the rabbits are
exposed to high temperatures during the hot season. The impact of temperature rabbits has
been studied by various authors. Lebas et al (1986) noted that high temperature
affects spermatogenesis, reducing the volume and concentration of ejaculates and also
affects sperm motility after 8 hours at 36 ºC or 14 days at 30ºC. High temperature also
affects growing rabbits negatively due to reduced rates of liveweight gain caused by the
reduction in feed intake. When rabbits are raised at 18-20 ºC they can reach a live
weight of 3 kg by 112 days, whereas at 30-31 ºC they only reach 2.5 kg (Lebas et al 1986).

It has been proposed that the system of underground shelters, developed
by Finzi and Amici (1991), would be a way of modifying the immediate environment of the
rabbit and thus make it possible to increase productivity in a tropical climate. This
paper reports the results of a preliminary experiment to test this hypothesis carried out
on small scale farms in Ha Tay and Hai Hung provinces in North Vietnam.

Material and methods

Housing system

Conventional:

The most widespread housing system in Vietnam is the one which utilizes
hutches or cages. This was introduced during the colonial period and imitates the hutch
models which were developed during the first phase of intensification of rabbit
production, and were later superceded by the wire net cages presently employed in large
scale operations world wide.

Alternative systems:

Free range

The free range system is obviously the most simple since it respects
the rabbit's natural living conditions. In a small group (1 buck and 3-5 does) the rabbits
will reproduce without leaving the area if feed and water are regularly supplied and they
are kept under control by some form of periphery fence.

Underground shelter

The underground shelter is based on the premise that rabbits under
natural conditions live in underground "burrows" dug out from the soil. This can
provide a better environment for the rabbits especially if they are free to move in and
out according to the climatic conditions.

The simulation of such "burrows" can be done by making a
shelter above or under the ground using stones, bricks, clay or concrete, which can be
covered by earth. With this system rabbits can choose the place to make their nest for
giving birth. They can also modify the shelter by "digging" to enlarge or
lengthen the "burrow".

Integrated free range and underground system

The integration of the underground shelter and limited free range
appears to be the most feasible way for implementing an improved housing system at
household level. This was the housing system chosen for the experiment.

Treatments, design and feeding

Thirty farmers, who traditionally raised rabbits, were chosen to
implement the experiment which consisted of a comparison of some form of underground
shelter versus the conventional system of raised wire cages. Each farmer was asked
to keep 3 females and 1 male for the observation of reproduction and lactation and 5
weaned rabbits for fattening on each of the two housing systems.

For the underground shelter, the farmers themselves decided on the
exact form in which the shelters were constructed following the principle of a fenced free
area of about 0.5-1 m² per adult rabbit and a mound of earth (0.5 x 2 m area and 0.5 m
high) in which the rabbits could make their "burrows". The mound area and the
immediate points of entry to the burrows were protected with a roof usually made of dry
leaves of sugar cane or rice straw to avoid rain entering the shelters.

The conventional housing consisted of cages made of wire or bamboo with
0.6 m² area per adult. Nest boxes were introduced into the cage immediately prior to
parturition.

The feeding system was the same for both types of housing and consisted
of free access to a molasses block, by-products from the kitchen as available (eg: banana
peel, jackfruit, soya bean residue), grasses (mostly guinea grass) and tree leaves (from Trichantera
gigantea, mulberry, Leucaena leucocephala and bamboo).

The experiment began in January 1996 and continued until July 1996.

A more detailed study of the effects of the housing system on
temperature and humidity was done between 5 and 15 July 1996 at the experimental farm of
the Goat and Rabbit Research Centre, where the same treatments as on the farms were
applied.

Measurements

On all farms the following performance data were recorded:

Liveweight of the does at the beginning and 2 months later

Litter size at birth and at weaning

Liveweight of growing rabbits at 1, 2 and 3 months of age

On the experimental farm, the ambient temperature and the humidify were
recorded daily at 7:00 , 13:00 and 19:00 hours in the cages and in the underground
shelters over a 10-day period from 5 to 15 July.

Results and discussion

Effect of housing systems on reproduction and growth of rabbits

The results from the on-farm trials are presented in Table 1. All the
performance parameters were significantly improved in rabbits housed in the underground
shelters compared with the cages. The does in underground shelters were 8% heavier after 2
months in the experiment, they gave birth to 39% more offspring and weaned 60% more than
those in cages. Survival rate to weaning of the offspring was improved by 16%.

Table 1: Mean values
for parameters of reproduction and growth of rabbits housed in cages or in underground
shelters in small scale farms

Cages

Under-

SE/Prob.

ground

Liveweight of doe, g

Initial

1652

1659

±20.9/NS

Final

2,137

2,310

±11.2/0.001

Litter size at

Birth

4.88

6.68

±0.13/0.001

Weaning

3.64

5.81

±0.11/0.001

Survival, %

74.1

85.7

±0.68/0.001

Weight of growing
rabbit, g

1 month

306

360

±3.9/0.001

2 month

891

1,055

±5.3/0.001

3 month

1,365

1,639

±6.5/0.001

Gain

1-3mth, g/d

17.7

21.3

±0.095/0.001

During the growing-fattening phase, the rabbits in underground shelters
were 17% heavier after 1 month and 19% heavier after 3 months with average growth rates
that were 20% greater.

It was not possible to obtain detailed records on feed intake but most
of the farmers observed that the rabbits in the underground shelters ate more than those
in cages. More precise experiments are needed to confirm this aspect.

Effect of housing systems on temperature and humidity

The results of the study on temperature and humidity during a 10-day
period in July in the two housing systems are shown in Tables 2, 3 and 4. Ambient
temperature on average was 3.8 ºC lower (P=0.001) and humidity was 4.75% higher (P=0.001)
in the underground shelters compared with the cages. It seemed that these mean differences
were maintained throughout the day from 7:00 to 19:00 hours (Table 3).

Table 2: Mean values
for temperature and humidity in cages and in underground shelters (at 00.70, 13.00 and
19.00 hours during a 10 day period

Day

Temperature

°C

Humidity, %

Grnd

Cage

Grnd

Cage

1

28

32

65

60

2

30

35

65

62

3

28

30

76

72

4

26

28

86

80

5

26

30

83

83

6

26

30

82

72

7

26

30

82

74

8

26

30

83

76

9

27

32

84

83

10

27

31

83

80

Table 3: Effect of
housing on temperature and humidity (mean values)

Cage

Grnd

Diff

SE/Prob

Temperature,ºC

29.4

25.9

3.8

±0.33/0.001

Humidity, %

75.9

80.4

4.75

±0.99/0.001

Table 4: Mean values
for temperature and humidity during the day in cages and underground shelters

Temperature

°C

Humidity, %

Cage

Grnd

Cage

Grnd

07.00

29.6

25.7

77.6

81.5

13.00

30.5

26.9

74.2

78.9

19.00

28.2

25.2

76.0

80.8

Conclusions and recommendations

The underground housing system for rabbits appears to be markedly superior to the
conventional cage system in North Vietnam at least during the hot summer period from April
to August as both reproduction and growth parameters were considerably improved by the new
housing system.

It is recommended that the system be evaluated throughout Vietnam especially at
smallholder level.

Acknowledgments

This study was financed through a "Letter of Agreement" with
the Animal Production and Health Division of FAO. The authors are grateful to Dr Manuel
Sanchez, FAO, Rome and to Dr A Finzi of the Rabbit Research Centre, Animal Husbandry
Institute, University of Viterbo, Italy, for their suggestions and advice.